This invention relates to a process for the production of polyalcohols, particularly xylite (or xylitol as it is sometimes termed) from the wood of deciduous trees or annual plants by decomposition with dilute mineral acid at elevated temperatures, decolorization and deionization with ion exchangers, and hydrogenation.
Numerous processes are known to produce in particular xylose and xylite from the wood of deciduous trees or from annual plants. Most of the processes, especially those practiced on an industrial scale, comprise the following series of process steps (Cf. Die Hefen, Volume II, Pages 82 to 113 (1962); Festkrift TILLAGNAD GUNNAR SUNDBLAD, Oct. 10, 1958, Ivar Haeggstroms Boktryckeri AB, Pages 75ff; West German Auslegeschriften Nos. 16 43 940; 25 30 386 and 23 50 668; and French Pat. No. 14 77 305):
1. Acid hydrolysis of the plant material with dilute mineral acids, especially sulfuric acid or hydrochloric acid, at temperatures of 100.degree. to approximately 135.degree. C.
2. Neutralization with lime and gypsum filtration (only in the case of sulfuric acid hydrolysis).
3. Removal of salts, organic acids, especially acetic acid, and coloring matter by means of ion exchangers, carbon and decolorizing resins.
4. Evaporation and crystallization of xylose.
5. Hydrogenation of xylose with Raney nickel at 30 to 50 atmospheres after previously adjusting the pH. Usually the xylose mother-liquor is also hydrogenated to polyalcohols.
6. Repeated deionization and evaporation of the xylite solution or the polyalcohol solution as the case may be.
7. Crystallization and drying of the xylite.
Variants of the above-described process steps additionally consist of an alkaline, acid or alcoholic prewashing prior to the actual hydrolysis, as may be seen for example, in the German Offenlegunsschriften Nos. 23 58 407 and 25 22 761. The process of the present invention does not require these process steps.
In any of these cases, the production of xylite on an industrial scale is only possible in a series of numerous process steps with concomitant high production costs. To date, this has prevented widespread use of this sugar substitute, even though its pleasant taste, its sweetening power comparable to sucrose, its acceptability for diabetics and especially its proven anticaries properties and unobjectionable nature from a health standpoint, make xylite a highly interesting substance from an economic viewpoint.